Thermospheric responses to gravity waves arising from mesoscale convective complexes

We employ a linear model of the responses to local body forces to estimate the spectra of gravity waves arising due to vertical motions within mesoscale convective complexes (MCCs) at equatorial latitudes. Ray tracing methods are then used to propagate these spectra through model wind and temperature fields and to anticipate their thermospheric effects. We find that gravity wave forcing by MCCs is dominated by large vertical motions of limited horizontal extent, that individual convective cells within an MCC effectively act as independent sources of gravity waves if they are separated by two or more diameters, and that vertical body forces create higher-frequency gravity waves than comparable horizontal body forces. Ray tracing reveals that of the gravity waves excited by MCCs, only the high-frequency, long-vertical-wavelength portions of the refracted spectrum (above the shear) can penetrate to high altitudes, that variable winds impose significant anisotropy on the surviving gravity waves, that refraction and dissipation determine the portion of the MCC wave spectrum important in the lower thermosphere, and that large net momentum flux divergence may lead to strong local body forcing well into the thermosphere. Gravity waves excited by MCCs and having sufficiently large vertical wavelengths and group velocities above the shears at lower altitudes can penetrate to altitudes at which they may be expected to contribute to the seeding of equatorial spread F. (C) 2004 Elsevier Ltd. All rights reserved.